Prehistoric and historic distributions of the critically endangered Mediterranean monk seal (Monachus monachus) in the eastern Atlantic

The present Atlantic range of the Mediterranean monk seal (Monachus monachus), a critically endangered species, comprises two populations in the Desertas Islands and Cape Blanco region. The species is currently the subject of an action plan that encourages the recolonization of its former range. I investigated their causes of its disappearance using species records from paleo‐archeological sites and historical sightings/toponyms. I hypothesize that the species' prehistoric range extended from the continental coasts of North Africa to the Iberian Peninsula, an area larger than its current known range. It is further hypothesized that the historic range included at least 13 colonies, seven more than the present number; and that the original optimal breeding habitat was open beaches, while sea caves were a suboptimal, marginal habitat. It is suggested that hunting and the disappearance of two islands due to a historical tsunami event explain the disappearance of the other populations, leaving only those at the Desertas Islands and Cape Blanco that were sheltered in sea caves. Furthermore, the use of sea caves, in conjunction with effective legal protection in the 20th century, explains the present‐day survival of these Atlantic colonies of M. monachus.     

The east‐west‐north colonization history of the Mediterranean and Europe by the coastal plant Carex extensa (Cyperaceae)

Coastal plants are ideal models for studying the colonization routes of species because of the simple linear distributions of these species. Carex extensa occurs mainly in salt marshes along the Mediterranean and European coasts. Variation in cpDNA sequences, amplified fragment length polymorphisms (AFLPs) and simple sequence repeats (SSRs) of 24 populations were analysed to reconstruct its colonization history. Phylogenetic relationships indicate that C. extensa together with the South American Carex vixdentata and the southern African Carex ecklonii form a monophyletic group of halophilic species. Analyses of divergence times suggest that early lineage diversification may have occurred between the late Miocene and the late Pliocene (Messinian crisis). Phylogenetic and network analyses of cpDNA variation revealed the monophyly of the species and an ancestral haplotype contained in populations of the eastern Mediterranean. The AFLP and SSR analyses support a pattern of variation compatible with these two lineages. These analyses also show higher levels of genetic diversity and differentiation in the eastern population group, which underwent an east‐to‐west Mediterranean colonization. Quaternary climatic oscillations appear to have been responsible for the split between these two lineages. Secondary contacts may have taken place in areas near the Ligurian Sea in agreement with the gene flow detected in Corsican populations. The AFLP and SSR data accord with the ‘tabula rasa’ hypothesis in which a recent and rapid colonization of northern Europe took place from the western Mediterranean after the Last Glacial Maximum. The unbalanced west‐east vs. west‐north colonization may be as a result of ‘high density blocking’ effect.     

Sewage pollution and extinction risk: an endangered limpet as a bioindicator?

The mollusc Patella ferruginea, endemic to the Mediterranean, is the most endangered marine species on the list of the European Council Directive 92/43/EEC and it is under serious risk of extinction. In spite of the low abundances and restricted distribution of this limpet, important populations have been found in the harbour of Ceuta, north Africa. The main objective of the present study was to characterise, for the first time, the effects of sewage pollution on P. ferruginea and related limpet species, and to evaluate the potential value of these limpet assemblages as bioindicators, using univariate and multivariate analyses. Physicochemical parameters and limpets were sampled in nine stations located at 0, 1, 2, 4, 8, 16, 32, 64 and 128 m away from the discharge point of a sewage effluent in Ceuta harbour. The stations closer to the outfall (0, 1, 2, 4 and 8) were characterised by higher values of turbidity, phosphate and ammonia in the water column, and organic matter, faecal coliforms and faecal Streptococci in sediments. A total of six limpet species were found and studied (Patella ferruginea, P. caerulea, P. nigra, P. rustica, P. ulyssiponensis and Siphonaria pectinata); the number of limpet species increased with increasing distance from the outfall, while diversity and evenness reached the highest values at intermediate sites. Siphonaria pectinata and P. caerulea were the most resistant and abundant species, while P. ferruginea was the most sensitive species to sewage pollution, only found at stations from 32 to 128 m. The distribution of this endangered limpet seems mainly affected by the pollution gradient, and not by the competition with the remaining limpets. The results of this study should be taken into account in future programmes of management and conservation of P. ferruginea.     

The Orange River avifauna: abundance,richness and comparisons

Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 deter-mined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Haliaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31 -3 4 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been over-looked as wetland habitats, and further avifaunal surveys of all of them are recommended.     

A new vertebrate for Europe: the discovery of a range‐restricted relict viper in the western Italian Alps

We describe Vipera walser, a new viper species from the north‐western Italian Alps. Despite an overall morphological resemblance with Vipera berus, the new species is remarkably distinct genetically from both V. berus and other vipers occurring in western Europe and shows closer affinities to species occurring only in the Caucasus. Morphologically, the new species appear to be more similar to V. berus than to its closest relatives occurring in the Caucasus, but can be readily distinguished in most cases by a combination of meristic features as confirmed by discriminant analysis. The extant population shows a very low genetic variability measured with mitochondrial markers, suggesting that the taxon has suffered a serious population reduction/bottleneck in the past. The species is extremely range‐restricted (less than 500 km²) and occurs only in two disjunct sites within the high rainfall valleys of the Alps north of Biella. This new species should be classified as globally ‘endangered’ due to its small and fragmented range, and an inferred population decline. The main near‐future threats to the species are habitat changes associated with reduced grazing, along with persecution and collecting.     

Climate hindcasts: exploring the disjunct distribution of Diopatra biscayensis

The ecosystem engineer onuphid polychaete Diopatra biscayensis has a continuous population in the Bay of Biscay from the Cantabria coast in Spain to southern Brittany in France. A group of disjunct populations also are found in the English Channel, separated from the Biscay population by more than 400 coastal kilometers. It remains unclear whether D. biscayensis is native to the Bay of Biscay; it is also debated whether the disjunct populations in the English Channel are relics of a formerly continuous population, or the product of recent introductions through aquaculture. Here, we use climate hindcasts to explore hypotheses about the D. biscayensis historical distribution in Europe. If D. biscayensis is native, its range would have been restricted to southern Iberia and the Mediterranean during the Last Glacial Maximum (21,000 BP). However, the species is completely absent from both regions today, further supporting its interpretation as a non‐native species. If it was historically present in Europe, the climate hindcasts are congruent with range contraction in the Last Glacial Maximum (21,000 BP), expansion in the Mid‐Holocene Warm Period (6000 BP), and contraction again in the past 1000 years (850–1850), prior to the first reports of D. biscayensis on the Spanish and French Atlantic coasts. However, the simulations do not support there being climatic refugia along the English Channel coast that would account for the existence of relic populations. Taken together, the evidence suggests that D. biscayensis has been introduced to the Bay of Biscay, and that disjunct populations in the English Channel are the result of recent transport through human activities, perhaps aquaculture.     

Phylogeography of the marine isopod Stenosoma nadejda (Rezig, 1989) in North African Atlantic and western Mediterranean coasts reveals complex differentiation patterns and a new species

The transition zone between the Mediterranean and Atlantic basins has been extensively addressed in phylogeographical studies of marine species. However, biases exist towards the analysis of highly dispersive species, and there is a higher sampling effort in European coasts compared to North Africa. This may be hindering a detailed understanding of the historical and contemporary processes that shaped patterns of population genetic structure in the region. In the present study, we investigated the phylogeographical and phylogenetic patterns of mitochondrial cytochrome c oxidase subunit I sequences from a species with direct development and low dispersal abilities, Stenosoma nadejda (Rezig, 1989). The study area included 13 localities along the Atlantic and Mediterranean North African coasts, as well as the Alboran Sea. A new Stenosoma species, from the coasts of Algeria and Alboran Island, was discovered. For S. nadejda, phylogeographical analyses revealed three distinct clades: one in the Iberian Atlantic plus the Alboran Sea, one in the western Mediterranean, and another in the Atlantic coast of Africa. Haplotypes from the Alboran Island were more related to those from the western Mediterranean coast (east of the Almeria–Oran Front). Given the strong differentiation, it is probable that this species survived in multiple glacial refugia during the Pleistocenic glaciations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 419–431.     

Spangled perch (Leiopotherapon unicolor) in the southern Murray‐Darling Basin: Flood dispersal and short‐term persistence outside its core range

The spangled perch Leiopotherapon unicolor is considered a rare vagrant in the southern Murray‐Darling Basin, Australia, due to its intolerance of the relatively cool water temperatures that prevail during winter months. This study details 1342 records of the species from 68 locations between 2010 and 2014 outside its accepted ‘core adult range’ following widespread flooding during 2010 and 2011. Although records of the species declined over 2013, L. unicolor remained resident in the southern Murray‐Darling Basin as of April 2014. The species persisted in several locations for three consecutive winters with recruitment documented at two sites. This study represents the first identification of the dispersal of large numbers of L. unicolor into the southern Murray‐Darling Basin, persistence beyond a single winter, and recruitment by the species in habitats south of its recognized ‘core adult range’. Targeted research would determine the potential for predicted environmental changes (artificially warmer drainage wetlands, climate change and greater floodplain connectivity) to facilitate longer term persistence and range expansion by the species in the southern Murray‐Darling Basin.     

Statistical power of replicated helicopter surveys in southern African conservation areas

Understanding the ecology of large ungulates in southern Africa requires accurate and precise measures of population size. Recovery or exploitation of ungulates in reserves is currently instigated when population size changes exceed 15% per annum, but monitoring is usually undertaken with single counts from helicopters, for which precision and the power to detect change are untested. In essence, power being the strength of a monitoring result in showing change over time. Retrospective power analysis is a useful technique to investigate the variability of single‐count aerial surveys. Using replicated helicopter‐based counts of southern African ungulates and post hoc analysis, we investigated the power of currently used single‐count surveys across five common ungulate species and 11 wildlife reserves. We expected high variability in count data and set α = 0.1 and 0.2 (α being the type I error rate), and asked two questions: ‘How much does power vary in replicated aerial counts of southern African wildlife across reserves and species?’ and ‘Can current single‐count aerial surveys detect population changes in response to management actions or are the statistical errors intractable?’ Single counts were mostly unreliable; only one of 42 had sufficient power to detect meaningful changes in population size or their trends at α = 0.1, and only three had sufficient power at α = 0.2. Power varied widely according to species (e.g. warthog, median power at α = 0.1; 0.12–0.37: blue wildebeest, median power at α = 0.1; 0.23–0.74), and, within species, between replicates and reserves. Our retrospective calculations demonstrated insensitivity and ineffectiveness in most currently applied single counts from helicopters. Consequently, it is impossible to interpret the effects of ungulate conservation actions on many southern African reserves. Retrospective power analyses enables determination of which previous aerial surveys were useful for population assessment and adaptive management, and which should be discarded. We recommend that prospective power analyses are undertaken to determine future helicopter survey sample size and replication requirements, especially in small reserves.     

Fistularia commersonii in the Mediterranean Sea: invasion history and distribution modeling based on presence-only records

The bluespotted cornetfish (Fistularia commersonii) (Osteichtyes, Fistulariidae) is considered to be one of the most invasive species of the Mediterranean Sea and Europe but only scattered information exists on its distribution and abundance. Here we collated the available species records, following its first detection in the Mediterranean Sea, in January 2000, until October 2011. A total of 191 observations were used to reconstruct the invasion sequence, to provide estimates of the rate of spread and to construct an environmental suitability model based on six biophysical variables and the maximum entropy approach. The results showed that colonization of the Mediterranean Sea proceeded in parallel along the southern and northern rim of the Basin at speeds that reached 1,000–1,500 km year^?1 with a clear decrease in the rate of spread at the Sicily Strait. The most important explanatory variables for describing the distribution of F. commersonii were mean depth (explaining 32.4 % of the data variance), chlorophyll-a (29.3 %), and salinity (18.4 %). Coastal areas with relatively low chlorophyll-a concentrations and high salinity were the preferred habitat of the bluespotted cornetfish in its invaded range. Conversely, extreme productivity (highly eutrophic or highly oligotrophic), low salinity and cold temperatures provided abiotic resistance to this invasion. Areas of high environmental suitability were identified along the northern coasts of the Levantine Sea, Dodecanese, Sicily Strait and Tyrrhenian Sea. In contrast, the north Aegean Sea, the Adriatic and the Alboran Sea, the Nile Delta, the western coasts of Egypt and Cyrenaica were unfavourable for the invasion. Despite some limits due to the model’s resolution scale, these general predictions provide new insights into the F. commersonii invasion, indicating abiotic factors of primary importance in shaping the distribution of this species in its invaded range.     

Migration and wintering strategies in vulnerable Mediterranean Osprey populations

A broad range of migration strategies exist in avian species, and different strategies can occur in different populations of the same species. For the breeding Osprey Pandion haliaetus populations of the Mediterranean, sporadic observations of ringed birds collected in the past suggested variations in migratory and wintering behaviour. We used GPS tracking data from 41 individuals from Corsica, the Balearic Islands and continental Italy to perform the first detailed analysis of the migratory and wintering strategies of these Osprey populations. Ospreys showed heterogeneous migratory behaviour, with 73% of the individuals migrating and the remaining 27% staying all year round at breeding sites. For migratory individuals, an extremely short duration of migration (5.2 ± 2.6 days) was recorded. Mediterranean Ospreys were able to perform long non‐stop flights over the open sea, sometimes overnight. They also performed pre‐ and post‐migratory trips to secondary sites, before or after crossing the sea during both autumn and spring migration. Ospreys spent the winter at temperate latitudes and showed high plasticity in habitat selection, using marine bays, coastal lagoons/marshland and inland freshwater sites along the coasts of different countries of the Mediterranean basin. Movements and home‐range areas were restricted during the wintering season. The short duration of trips and high levels of variability in migratory routes and wintering grounds revealed high behavioural plasticity among individuals, probably promoted by the relatively low seasonal variability in ecological conditions throughout the year in the Mediterranean region, and weak competition for non‐breeding sites. We stress the importance of considering the diversity in migration strategies and the particular ecology of these vulnerable populations, especially in relation to proactive management measures for the species at the scale of the Mediterranean region.     

Presence of Caulerpa racemosa (Forsskål) J. Agardh in Ceuta (Northern Africa, Gibraltar Area)

Caulerpa racemosa (Forsskål) J. Agardh has been recorded along the Mediterranean Sea since the 1920s, and since then has continually invaded its coasts moving westward towards the Atlantic. In recent years, authors have revealed the negative effect of the species on the Mediterranean’s benthic communities. Taking into account that the latest reference placed the species in Murcia (Southeastern Spain) in 2005, we now give evidence here of the presence of this invasive algae in Ceuta, a Spanish city located in the Strait of Gibraltar on the North Africa Coast. This is the first and westernmost recorded presence of the species in the area. Characteristics of the located patches are given.     

Limits of pine forest distribution at the treeline: herbivory matters

Herbivores can affect future forest composition by feeding selectivity. At temperature-sensitive treelines, herbivory can exacerbate or constrain climate-driven distributional shifts in tree species. This study analyses the impact of herbivory in a Mediterranean treeline of widespread Pinus sylvestris and P. nigra pinewoods, testing whether herbivory damage reinforces or inhibits the climatic responses of these trees. We used naturally occurring sapling pairs of similar size and age of both species, thereby isolating plant characteristics from environmental effects in herbivore behaviour. Herbivory damage by ungulates proved higher than that caused by insects in saplings of both species. Low plant density and extreme abiotic conditions at the treeline could in part be responsible for the observed low incidence of insect herbivory. Ungulates preferred P. sylvestris over P. nigra, implying heavier browsing damage for a large number of P. sylvestris saplings, suffering reduced internode growth as a consequence. In addition, P. sylvestris could not compensate height-growth reductions due to browsing with higher growth rate than P. nigra. In fact, P. sylvestris showed similar or lower relative height growth with respect to P. nigra. Under a scenario of increasing aridity and maintenance of ungulate populations, the upward migration of P. sylvestris in its southern range could be restricted by higher drought vulnerability than P. nigra, a situation exacerbated by ungulate herbivory. Our results indicate that ungulate herbivory reinforces climatic response of coexisting P. sylvestris and P. nigra at treeline, favouring a potential change in community dominance towards Mediterranean P. nigra.     

Population genetics of the endangered limpet Patella ferruginea (Gastropoda: Patellidae): taxonomic, conservation and evolutionary considerations

The limpet Patella ferruginea is the most endangered marine invertebrate in the western Mediterranean rocky shores, whereas Patella caerulea is the most common Mediterranean limpet. From Pleistocene to historic age, P. ferruginea was distributed around the whole Mediterranean basin, since the shells of this species are a characteristic feature of Palaeolithic and Neolithic deposits in this area. However, its Mediterranean range has progressively contracted to a few restricted areas. The ancient origin of the species (18 Ma) and the present geographical isolation among relic populations could have led to a great genetic difference among populations, taking into account the supposedly low dispersal ability of the species. However, we have observed a few genetic differences among populations and a 'star phylogeny' of COI haplotypes from the 41 individuals of P. ferruginea analysed; a similar pattern has also been observed for the seven individuals of P. caerulea studied. Genetic evidences show a possible bottleneck event on late Pleistocene that affected the two species. The results have an important implication on the future management of this endangered species. Additionally, two different morphological types of P. ferruginea have been described by Payraudeau in 1826 : lamarcki and rouxi forms. Clear morphological differences occur between these two types and some authors pointed out the hypothesis about the existence of two different species. The results of the present study conclude that the two different forms of P. ferruginea are ecotypes, rather than different species or subspecies, and intermediate steps are an ecological range instead of hybridization events among different species.     

Where and how Argentine ant (Linepithema humile) spreads in Corsica?

The Argentine ant, Linepithema humile (Dolichoderinae), is one of the most widespread invasive ant species in the world. When established in optimal habitat, this species usually excludes most other local ants and can heavily impact other arthropods as well. Although Argentine ants have been present in southern Europe for more than 100 years, they were first noted in Corsica, a French Mediterranean island, in 1957 in only one urban station. In this study, we aimed to map precisely their geographical distribution in Corsica and to quantify their presence by using an infestation index. We recorded changes in the distribution of Argentine ants in Corsica over the past decade. Argentine ants appeared to be well established within their introduced range and spreading along the Corsican coasts principally through Human-mediated jump-dispersal but not homogenously. To cite this article: O. Blight et al., C. R. Biologies 332 (2009).     

Evaluation of biodiversity and conservation strategies in <Emphasis Type="Italic">Pancratium maritimum</Emphasis> L. for the NorthernTyrrhenian Sea

Pancratium maritimum L. is an Amaryllidaceous species whose presence is severely endangered in its original range, the sandy coasts of the Mediterranean sea. A molecular analysis has been performed to evaluate the genetic distance among populations coming from different locations, in order to define the best repopulating strategy. The plant genome, analysed by AFLP markers, was found to be extremely homogeneous and conserved, evoking vegetative or autogamous reproductive habits. Seeds from two different locations showed a good germination capability in greenhouse tests, indicating the potential presence of an efficient sexual reproduction. The combination of molecular data and germination tests would support the hypothesis of an autogamous reproduction for this species.     

The geography of speciation in narrow‐range endemics of the ‘Haenydra’ lineage (Coleoptera,Hydraenidae, Hydraena)

Aim We test whether species of western Mediterranean aquatic Coleoptera of the ‘Haenydra’ lineage (Hydraenidae, Hydraena) originated through: (1) successive periods of dispersal and speciation, (2) range fragmentation by random vicariance, or (3) range fragmentation by geographic isolation owing to a general reduction of population density. Location Europe. Methods To discriminate between scenarios we use contrasting predictions of the relationship between phylogenetic and geographic distance. The phylogeny was based on 3 kb of four mitochondrial and two nuclear gene fragments of about half of the known species of ‘Haenydra’, including most western Mediterranean taxa. Divergences were estimated using a molecular clock. The relationship between phylogenetic and geographic distance was tested using bivariate plots, Mantel tests and comparison of the observed phylogeny with the one minimizing geographic distances between species, as measured using Euclidean minimum spanning trees (EMSTs). Results The monophyly of ‘Haenydra’ was strongly supported, although its phylogenetic placement was not resolved. ‘Haenydra’ was estimated to be of late Miocene age, with most species originating during the Pleistocene. In two clades (Hydraena tatii and Hydraena emarginata clades) there was a significant association between geographic and phylogenetic distance, and the reconstructed phylogeny was identical to that obtained through the EMST, demonstrating a strong non‐randomness of the geographic distribution of the species. In two other clades (Hydraena iberica and Hydraena bitruncata clades) there was no association between geographic and phylogenetic distance, and the observed phylogeny was not the one minimizing geographic distances. In one of the clades this seems to be due to a secondary, recent range expansion of one species (H. iberica), which erased the geographic signal of their distributions. Main conclusions We show that it is possible to obtain strong evidence of stasis of the geographic ranges of narrow‐range endemic species through the study of their phylogenetic relationships and current distributions. In at least two of the studied clades, current species seem to have originated through the fragmentation of a more widely distributed species, without further range movements. A process of range expansion and fragmentation may have occurred repeatedly within the ‘Haenydra’ lineage, contributing to the accumulation of narrow‐range endemics in Mediterranean Pleistocene refugia.     

Genomic signatures of rapid adaptive evolution in the bluespotted cornetfish,a Mediterranean Lessepsian invader

Biological invasions are increasingly creating ecological and economical problems both on land and in aquatic environments. For over a century, the Mediterranean Sea has steadily been invaded by Indian Ocean/Red Sea species (called Lessepsian invaders) via the Suez Canal, with a current estimate of ~450 species. The bluespotted cornetfish, Fistularia commersonii, considered a ‘Lessepsian sprinter’, entered the Mediterranean in 2000 and by 2007 had spread through the entire basin from Israel to Spain. The situation is unique and interesting both because of its unprecedented rapidity and by the fact that it took this species c. 130 years to immigrate into the Mediterranean. Using genome scans, with restriction site‐associated DNA (RAD) sequencing, we evaluated neutral and selected genomic regions for Mediterranean vs. Red Sea cornetfish individuals. We found that few fixed neutral changes were detectable among populations. However, almost half of the genes associated with the 47 outlier loci (potentially under selection) were related to disease resistance and osmoregulation. Due to the short time elapsed from the beginning of the invasion to our sampling, we interpret these changes as signatures of rapid adaptation that may be explained by several mechanisms including preadaptation and strong local selection. Such genomic regions are therefore good candidates to further study their role in invasion success.     

A phylogeographic investigation of the kelp genus Laminaria (Laminariales,Phaeophyceae), with emphasis on the South Atlantic Ocean

The genus Laminaria has a wide distribution range compared with other kelp genera because it is found in both the North and the South Atlantic, on both sides of the North Pacific, as well as in the Mediterranean. Hypotheses behind this biogeographical pattern have been discussed by several authors but have not yet been fully evaluated with time‐calibrated phylogenies. Based on the analysis of four molecular markers (ITS2, rbcL, atp8 and trnWI), our goal was to reassess the Laminaria species diversity in South Africa, assess its relationship with the other species distributed in the South Atlantic and reconstruct the historical biogeography of the genus. Our results confirm the occurrence of a single species, L. pallida, in southern Africa, and its sister relationship with the North Atlantic L. ochroleuca. Both species belonged to a clade containing the other South Atlantic species: L. abyssalis from Brazil, and the Mediterranean L. rodriguezii. Our time‐calibrated phylogenies suggest that Laminaria originated in the northern Pacific around 25 mya, followed by at least two migration events through the Bering Strait after its opening (~5.32 mya). Today, the first is represented by L. solidungula in the Arctic, while the second gave rise to the rest of the Atlantic species. The colonization of the North Atlantic was followed by a gradual colonization southward along the west coast of Europe, into the Mediterranean (~2.07 mya) and two recent, but disconnected, migrations (~1.34 and 0.87 mya) across the equator, giving rise to L. abyssalis in Brazil and L. pallida in southern Africa, respectively.     

The distribution of benthic marine algae in relation to the temperature regulation of their life histories

Mainly on the basis of the distribution patterns of 42 species of the recently revised genus Cladopkora (Chlorophyceae) in the north Atlantic Ocean, it appeared possible to distinguish 10 phytogeographic distribution groups of wide applicability. Experimentally determined critical temperatures limiting essential events in the life histories of 17 benthic algal species were used to infer possible phytogeographic boundaries; these appeared to fit closely the phytogeographic boundaries derived from field-distribution data. For a temperate species, at least six different boundaries can be postulated and should be checked in the northern hemisphere: (1) the ‘northern lethal boundary’ (corresponding to the lowest winter temperature which a species can survive); (2) the ‘northern growth boundary’ (corresponding to the lowest summer temperature which, over a period of several months, permits sufficient growth); (3) the ‘northern reproductive boundary’ (corresponding to the lowest summer temperature permitting reproduction over a period of several months); (4–6) the corresponding southern boundaries. Photoperiodic responses may influence the temperature responses. Many phytogeographic boundaries appear to be of a composite nature. For instance, the southern boundary of Laminaria digitata follows the European 10°C February isotherm (which corresponds to the highest winter temperature permitting fertility in the female gametophyte, i.e. to the ‘southern reproductive boundary’), and the American 19°C summer isotherm (corresponding to the ‘southern lethal boundary’). Thus, experimental evidence supports the validity of eight of the following 10 distribution groups (for distribution groups 2 and 6, such evidence could not be found): (1) the amphiatlantic tropical-to-warm temperate group, with a north-eastern extension (examples: Gracilaria foliifera and Centroceras clavulalum); (2) the amphiatlantic tropical-to-warm temperate group, with a north-western extension (example: Hypnea musciformis); (3) the amphiatlantic tropical-to-temperate group (example: Sphacelaria rigidula =furcigera); (4) the amphiatlantic temperate group: the Cladophora rupestris type (examples: Callithamnion hookeri, Dumontia contorta; Laminaria saccharina is transitional to type 10, I., digitata to types 5 and 10); (5) the amphiatlantic temperate group: the Cl. albida type (examples: Scytosiphon lomentaria, Petalonia fascia); (6) the tropical western Atlantic group; (7) the north-east American tropical-to-temperate group (example: Gracilaria tikvahiae); (8) the north-east American temperate group and the corresponding Japanese temperate group (examples: Campylaephora hypneoides and Sargassum muticum); (9) the warm-temperate Mediterranean-Atlantic group, and the corresponding warm-temperate Californian group (examples: Saccorhiza polyschides, Laminaria hyperborea, I., ockroleuca, Macrocystis pyrifera, Hedophyllum sessile); (10) the Arctic group (examples: Saccorhiza dermatodea and Sphacelaria arctica). Distribution groups 6, 9 and 10 have comparatively narrow temperature ranges with a span of 18 22°C between their lethal boundaries and of 5 12°C between their reproductive or growth boundaries. These narrow temperature ranges limit the species in these groups to the tropics; the temperate coasts on the eastern sides of the north Pacific and north Atlantic Oceans and in the southern hemisphere; and to the Arctic, respectively. The narrow temperature ranges of group 9 make the species in this group unfit for life on the western temperate coasts of the north Pacific and north Atlantic Oceans, where algae must cope with annual temperature fluctuations of more than 20°C. Conversely, algae in group 8 (containing the numerous Japanese endemic species) are characterized by wide temperature spans (e.g. 29°C between ‘lethal boundaries’, 12–19°C between ‘growth and/or reproductive boundaries’) and must be potentially capable of occupying wide latitudinal belts on temperate coasts along the east sides of the north Pacific and north Atlantic Oceans. Algae ‘escaped’ from Japan, such as Sargassum muticum, conform to this picture. Apparently Japanese algae do not have the capacity for long distance dispersal. The corresponding east American coasts (30–45 N) harbour very few endemic species, probably as a result of the adverse nature of these sediment coasts for benthic macroalgae and their functioning as a barrier to latitudinal displacements of the flora during glaciations. The remaining distribution groups (1,2,3,4,5,7) are characterized by wide temperature spans and wide distributions, often in both the Atlantic and Pacific Oceans and in both hemispheres. Six temperate species (in distribution groups 4, 5 and 9) with an amphiaequatorial distribution have similar winter-temperature maxima permitting reproduction and corresponding with winter isotherms of 15–17°C; their upper lethal temperatures are more dissimilar and correspond with summer isotherms of 20–30°C. Their amphiaequatorial distribution can be explained by assuming glacial temperature drops along east Pacific and east Atlantic equatorial coasts in narrow belts of intensified upwelling during the presumably intensified glacial circulation of the ocean gyres.